The disclosure of Japanese Patent Application No. 2001-233899 filed on Aug. 1, 2001 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of Invention
The invention relates to an apparatus that prevents hydrocarbons (HCs) of fuel or the like from being emitted outside from an intake system of an internal combustion engine (engine) and a method thereof.
2. Description of Related Art
Recently, from an environmental conservation point of view, a trend to reduce the HCs, which are emitted from an internal combustion engine mounted on a vehicle, have been increasing. Various studies have been made on unburned HCs that are emitted outside together with exhaust emissions and on HCs that evaporate from a fuel supply system such as a fuel tank and leaks outside. However, it is necessary to also pay attention to the HCs that flow outside through an air intake path of the intake system when the internal combustion engine is stopped. HCs that flow out from the intake system include HCs of unburned fuel (xe2x80x9can intake port wetxe2x80x9d, xe2x80x9can cylinder wetxe2x80x9d or the like) that is adhered to a wall surface of the inside of the intake port and/or a cylinder in the form of an oil film during operation of the internal combustion engine and the HCs of fuel, engine oil or the like contained in blowby gas that is recirculated to the intake system by a positive crankcase ventilation (PCV: compulsory air ventilation in crankcase) system. It is necessary to prevent these HC gases from leaking outside of the vehicle through the air cleaner or the like diffusing within the intake path after the internal combustion engine is stopped.
As one of the countermeasures against the problem above, it is proposed in Japanese Utility Model Laid-Open No. 63-157228 that a filter element containing activated carbon is formed by laying filter paper and activated carbon paper capable of adsorbing the HCs and folding them in bellows, and the filter element is mounted in place of an ordinary air cleaner element within an air cleaner provided in the intake path of an internal combustion engine.
However, in a filter element, which contains activated carbon as described above, when an amount of the activated carbon is increased, air flow resistance is increased resulting in an increased pressure loss. Accordingly, since a problem of an output decrease of the engine occurs, it is impossible for the filter element to carry a large amount of activated carbon. Consequently, since only a small amount of HCs is adsorbed by the activated carbon, when the fuel, which forms an oil film-like intake port wet and cylinder wet, absorbs residual heat of the internal combustion engine after the internal combustion engine is stopped, the fuel, in a form of a large amount of HC, evaporates and flows to the filter element at once. Then, the activated carbon is saturated and cannot adsorb the HCs any more. As a result, there is a possibility that HCs, that were not adsorbed, will flow out through an air intake path of the air cleaner.
Therefore, as a countermeasure against the problem above, it is necessary to prevent a large amount of HCs, which evaporates from the intake port wet and the cylinder wet, from reaching the filter element containing activated carbon by always fully closing a throttle valve disposed downstream of the filter element while the internal combustion engine is stopped (also by closing an idle speed control valve (ISCV) that bypasses the throttle valve if it is provided,) with an exception of a small amount of HCs, which leaks upstream through a narrow gap between the throttle valve and the surrounding throttle body. Since, in many internal combustion engines, the throttle valve is fully closed while the engine is stopped, this problem does not seem very critical.
However, in a case where the throttle valve is kept in a fully closed state when the internal combustion engine is stopped, the HCs contained in blowby gas, which is recirculated to the intake system by the PCV system during operation of the internal combustion engine, are likely to accumulate in a liquid state in a narrow gap of the fully closed throttle valve. It may be assumed that the above is caused by the capillarity. Further, since the blowby gas contains tar components and fine particles of carbon, the viscosity of the liquid HCs accumulated in the gap of the throttle valve is higher than the viscosity of the light fuel may be assumed as another cause.
When heat of the internal combustion engine, which is in a state of, so-called xe2x80x9cdead soakxe2x80x9d after the engine is stopped, is transmitted up to the periphery of the throttle valve. In addition, the temperature of the gap is increased, molecules of the HCs adhered to the gap of the throttle valve around the thus closed throttle valve are polymerized into a high polymer by the heat, resulting in a tar-like deposit having a high viscosity. Consequently, the throttle valve is stuck to the throttle body, thus preventing free movement. When this event is repeated, and when the throttle valve gets into a fixed state, not only the valve hardly works smoothly but a problem may occur that the valve opens suddenly, causing a rapid increase in the rotation speed of the internal combustion engine when a strong operating force is applied thereto.
The invention thus provides an apparatus and method that reduces the possibility of sticking of a throttle valve, and effectively prevent the HCs from leaking to the outside of a vehicle from an intake system without the need to increase the amount of the activated carbon as the air flow resistance.
The invention utilizes a time lag between a period of time that the HCs adhered to the throttle valve is heated and polymerized, and a period of time that the fuel adhered in a form of oil film to a wall surface of an intake port or a cylinder of the internal combustion engine evaporates and reaches the air cleaner. That is to say, the aforementioned problem is solved by opening the throttle valve after the internal combustion engine is stopped so as to prevent the HCs adhered to the gap of the throttle valve from being polymerized by heat and sticking the gap, and further by closing the throttle valve after the temperature around the throttle valve has been decreased to a level that the polymerization reaction of the HCs does not occur so as to seal the vapor of the HCs downstream of the throttle valve.
The first aspect of the invention relates to a hydrocarbons emission preventive apparatus in the intake system of the internal combustion engine. The apparatus includes a first throttle valve provided in the intake path and a controller that opens the first throttle valve after the internal combustion engine is stopped, keeps the valve open from a point of time when the throttle valve is opened until a predetermined condition is met where substantially no polymerization occurs by the hydrocarbons on at least one of the first throttle valve and the intake path surrounding the first throttle valve and closes the first throttle valve when the predetermined condition is met. Accordingly, for example, because it is possible to keep the throttle valve open for a predetermined period of time (for example, a period of time of 60 minutes or less) during which the HCs contained in the blowby gas and adhered to the gap of the throttle valve are polymerized by heat transmitted from a high temperature portion of the internal combustion engine after operation thereof is stopped, it is possible to prevent the throttle valve from sticking to the valve body by the polymerized HCs. When the period of time has passed, because the heat transmitted to the periphery of the throttle valve diffuses and the temperature around the throttle valve is also decreased, even when the throttle valve is closed, the problem of sticking does not occur.
Further, although the HCs evaporate from the oil-film like fuel adhered to the inside of a combustion chamber and an intake port, and diffuse upstream in the intake path after the internal combustion engine is stopped, it takes a considerably long period of time for the HCs to reach the throttle valve, and an inlet portion of the intake path such as an air cleaner provided further upstream. Accordingly, for example, even when the throttle valve is opened for a predetermined period of time as described above in order to avoid sticking of the throttle valve due to polymerization of the HCs after the internal combustion engine is stopped, the vapor of the HCs does not flow up to a position of the throttle valve. Therefore, by closing the throttle valve again after opening it for a predetermined period of time, it is possible to prevent the HCs that evaporated from flowing outside through the air intake path by sealing the HCs within a surge tank downstream of the throttle valve.
A second aspect of the invention relates to a method for preventing emission of hydrocarbons from being emitted through an intake path of the internal combustion engine. The method includes the steps of opening a throttle valve provided in the intake path after stopping the internal combustion engine, keeping the throttle valve open from a point of time when the throttle valve is opened until a predetermined condition is met where substantially no polymerization occurs by the hydrocarbons on at least one of the first throttle valve and the intake path surrounding the first throttle valve and closing the first throttle valve when the predetermined condition is met.